Technical Field
The present disclosure generally relates to the field of illumination devices and, more particularly, to the control of illumination levels of illumination devices.
Description of the Related Art
Energy conservation through the efficient usage of energy has become an important topic in recent years. Efficient usage of energy can result in a multitude of benefits, including financial benefits such as cost savings and environmental benefits such as preservation of natural resources and the environment. In the context of light systems, efficient energy usage by a lighting system is perhaps most effectively accomplished by reducing the illumination level when a high illumination level is not needed. This can be achieved manually by a user of the lighting system or, more conveniently, by some sort of automatic control mechanism that adjust the illumination level according to changes in certain environmental characteristics.
One conventional approach to automatic control of illumination level of lighting systems is to use a passive infrared (PIR) sensor to detect the presence of a human, indicative of the need of lighting. For example, the PIR sensor can be used to provide full power to a lamp when heat emitted by a human body is detected. PIR sensors, however, are not an ideal solution. This is because PIR sensors generally have a very short sensing range with a maximum sensing range of 10 meters typically. Many light poles are 10 meters tall, yet a PIR sensor in a lamp installed on top of a light pole needs to have a detection range much longer than the pole height in order to detect the presence of a person or a heat-emitting object at the periphery of the lighting area. Otherwise, the benefit of using a PIR sensor to automatically control the illumination level under such circumstances would likely be diminished. In addition, PIR sensors require a substantial difference between body temperature and the background ambient temperature for optimal sensitivity. Accordingly, at ambient temperatures approaching the normal temperature of a human body, PIR sensors tend to exhibit reduced sensitivity and thus effectively have a shortened detection range. Furthermore, PIR sensors typically cannot detect objects that are at ambient temperature, such as a door opening for example, although such an event usually indicates the approach of a person and is desirable to detect.